The present invention generally relates to the production of an ammonium octamolybdate composition, and more particularly to the manufacture of a novel and unique ammonium octamolybdate isomer having a number of beneficial characteristics.
Ammonium octamolybdate (hereinafter designated as "(NH.sub.4).sub.4 Mo.sub.8 O.sub.26 " or "AOM") is a commercially-useful molybdenum composition which is available in multiple forms or "isomers". Each isomer is characterized by its ability to differentially rotate and otherwise reflect light passing therethrough. In particular, two main isomers of AOM have been isolated and used commercially, namely, (1) the .alpha. form (".alpha.-AOM"); and (2) the .beta. form (".beta.-AOM"). Other isomers also exist including the .gamma. form (".gamma.-AOM") and the .delta. form (".delta.-AOM"). However, little information is available regarding the .gamma. and .delta. materials which are mostly generated in very small quantities as by-products and are predominantly theoretical/experimental in nature. Of particular interest from a commercial standpoint is the manufacture of .alpha.-AOM which is used as a smoke suppressant in many different compositions including polymeric plastic coating materials for electrical wiring and fiber-optic elements. Representative plastic materials suitable for combination with .alpha.-AOM include rigid polyvinyl chloride ("PVC"). The .beta.-AOM isomer is likewise secondarily useful for this purpose although .alpha.-AOM is preferred.
In general, .alpha.-AOM is traditionally produced by the thermal decomposition of ammonium dimolybdate which shall be designated hereinafter as "(NH.sub.4).sub.2 Mo.sub.2 O.sub.7 " or "ADM". This process occurs in accordance with the following basic chemical reaction: EQU 4(NH.sub.4).sub.2 Mo.sub.2 O.sub.7 +heat .fwdarw..alpha.-(NH.sub.4).sub.4 Mo.sub.8 O.sub.26 +4NH.sub.3 +2H.sub.2 O (1)
However, as noted in U.S. Pat. No. 4,762,700 (which is incorporated herein by reference), the foregoing process is characterized by numerous disadvantages including the generation of .alpha.-AOM having too large a particle size. As a result, the .alpha.-AOM product generated from reaction (1) listed above had to be physically size-reduced using conventional material-handling procedures which resulted in additional production costs and increased manufacturing time.
Another disadvantage associated with the conventional thermal generation of .alpha.-AOM involved the production of undesired by-products if the chemical reactants were improperly heated (e.g. over-heated or insufficiently heated according to U.S. Pat. No. 4,762,700). When this situation occurred, the following undesired by-products were generated: (1) ammonium trimolybdate (which is also characterized as "(NH.sub.4).sub.2 Mo.sub.3 O.sub.10 or "ATM") and (2) molybdenum trioxide (also designated herein as "molybdic oxide" or "MoO.sub.3). Since neither of these materials have the important and beneficial smoke-suppressive characteristics of .alpha.-AOM as discussed herein, they are undesired in the .alpha.-AOM production process. For this reason, the thermal decomposition method outlined above must be very carefully monitored, which again results in greater labor costs, more extensive processing equipment, and increased margins of error.
To overcome these disadvantages, an "aqueous" or "wet" reaction process was developed which is extensively discussed in U.S. Pat. No. 4,762,700 (again incorporated herein by reference). This process basically involves the initial combination of ammonium dimolybdate ("ADM" as previously noted) with water to yield a slurry-type mixture. In a preferred embodiment, about 50-350 grams of ADM are used per liter of water to form the desired mixture. Thereafter, particulate molybdenum trioxide is combined with the ADM-containing slurry, with the molybdenum trioxide having a preferred particle size of about 10-300 microns and a high purity level (e.g. not more than about 0.5% by weight (total) of iron (Fe), potassium (K), copper (Cu), lead (Pb), calcium (Ca), and other impurities.) It is further stated in U.S. Pat. No. 4,762,700 that both of these materials are specifically combined in the stoichiometric proportions set forth in the following basic formula: EQU 2(NH.sub.4).sub.2 Mo.sub.2 O.sub.7 +4MoO.sub.3 .fwdarw..alpha.-(NH.sub.4).sub.4 Mo.sub.8 O.sub.26 (2)
The initial ADM-containing slurry product used in the reaction listed above may be manufactured in many different ways including but not limited to a combination of water, ammonium hydroxide ("NH.sub.4 OH"), and molybdenum trioxide. The ADM-containing slurry product can be also derived from "ADM crystallizer mother liquor". Finally, commercially-available, pre-manufactured ADM can be directly combined with water to yield the slurry. Regardless of which process is employed for this purpose, U.S. Pat. No. 4,762,700 states that the molar ratio of ammonia to molybdenum (e.g. [NH.sub.3 ]/[Mo]) in the ADM-containing slurry should be adjusted to a value of 1.00 prior to addition of the particulate molybdenum trioxide so that the resulting .alpha.-AOM product is substantially free from undesired impurities including .beta.-AOM, ammonium heptamolybdate, and other non .alpha.-AOM compounds.
Regarding .beta.-AOM, this material is again generated as a side product in traditional thermal decomposition methods. While .beta.-AOM also has smoke suppressant properties, .alpha.-AOM is generally recognized as being superior for these purposes. Accordingly, .beta.-AOM has only secondary commercial value compared with .alpha.-AOM as previously noted.
Further information, data, and other important parameters regarding .alpha.-AOM and .beta.-AOM will be presented below from a comparative standpoint in order to illustrate the novelty of the present invention which involves a new AOM isomer. This unique isomer (designated herein as "X-AOM") differs considerably from all other forms/isomers of AOM including but not limited to .alpha.-AOM and .beta.-AOM (as well as the .gamma. and .delta. forms of AOM). As discussed in greater detail below, X-AOM is different from the other listed isomers both structurally and functionally.
In accordance with the information provided herein, .alpha.-AOM is traditionally used as a smoke control agent in plastic materials and other related compositions. However, the X-AOM isomer offers a number of benefits compared with traditional .alpha.-AOM including more efficient smoke suppression per unit volume and greater stability/uniformity. Furthermore, as confirmed by sophisticated chemical identification techniques (including a process known as "Raman spectral analysis" which will be summarized in further detail below), the claimed X-AOM product is likewise characterized by a novel isomeric structure which differs considerably from the structure of .alpha.-AOM and .beta.-AOM. The use of Raman spectral analysis enables the X-AOM product to be clearly identified and distinguished from other isomers of AOM. In addition, X-AOM is produced using a unique manufacturing process which facilitates the generation of this material in a highly-effective and preferential manner on production-scale levels.
For these and other reasons discussed in the Detailed Description of Preferred Embodiments section, the present invention represents a considerable advance in the art of ammonium octamolybdate production. The claimed invention specifically involves (1) the generation of a structurally novel isomeric AOM product which provides many important functional capabilities; and (2) the creation of a specialized manufacturing method which enables the X-AOM product to be produced in high yields with a considerable degree of purity. Accordingly, the present invention is novel, unique, and highly beneficial in many ways as outlined in greater detail below.